Nickel plating compositions and method



ilnit NllCKEL PLATING COMPUSITIONS AND lliETl-IQD John B. Winters, (Jleveland, and Leon R. Westbrook, Solon, Ohio, assignors to linear, Inc., (Cleveland, Ohio, a corporation of Ohio No Drawing. Application October 1, 1956 Serial No. 612,937

7 tClaims. (Cl. 204-49) This invention relates to the electrodeposition of nickel and is particularly directed to plating bath compositions from which bright, mirror-like nickel deposits are plated, consisting of aqueous solutions of nickel salts characterized by containing polyacrylamide; and to compositions of matter containing polyacrylamide for use as nickel plating bath addition agents.

it is an object of this invention to provide nickel plating bath compositions containing new and novel addition agents for producing bright, lustrous, mirror-like nickel electrodeposits direct from the plating bath.

It is another object of this invention to provide new and novel addition agent compositions for use in nickel electroplating baths.

Nickel, plated from the conventional plating bath formulations, is dull in appearance and needs mechanical bufling to produce a polished or shiny surface. It is common practice to add various organic compounds to such plating baths in order to produce bright, mirror-like deposits direct from the bath.

We have now found a class of chemical compounds that are particularly effective in producing bright, lustrous, mirror-like nickel deposits from aqueous solutions of nickel salts containing them, both alone and in combination with other materials that act in a synergetic manner. In addition, they greatly increase the throwing power and covering power of the bath, which means that nickel deposits more uniformly on the low and high current density areas of an irregularly shaped object, thus providing better coverage and protection on the low current density areas. We have also found that our new and novel addition agent causes nickel to be deposited in corners and recesses that cannot be covered in other bright nickel plating baths not containing them.

Our new and novel nickel plating addition agents can be classified as polymerized acrylamides and are generally called polyacrylamides, or more simply, polyacrylamide. The degree of polymerization is not important so long as the material is bath soluble, since the amount used in the bath can be adjusted to the degree of polymerization, if necessary to secure the results desired, all of which is familiar in principle to those skilled in the art.

Polyacrylamide acts as a brightener in all of the regular, well-known nickel plating solutions which in general, consist of aqueous solutions of nickel salts, such as, for example, the fluoborate, sulfate, chloride or sulfamate, either alone or more commonly in various combinations and concentrations, usually with boric acid as a bath constituent at concentrations up to saturation. Other substituent salts, such as, for example, the ammonium, sodium, or magnesium compounds of the foregoing acidic components can be included, if desired, for devious purposes, all of which is well known to those skilled in the art.

Without limiting ourselves to any specific nickel plating bath formulation or conditions of operation, all of which may be found in any of the standard references,

2,893,933 iatented July 7, 195.9

we may cite the following example as particularly effective and as illustrative of our invention:

Bath composition: Grams per liter Nickel sulfate, NiSO .7ll O 250 Nickel chloride, NiCl .6H O 60 Boric acid, H BO 45 Polyacrylamide 0.2

The concentration of polyacrylamide may vary over wide limits, depending on the degree of polymerization and bath solubility, as hereinbefore explained, but in general the optimum concentration usually will be found to be from about 0.05 to about 0.50 gram per liter of plating bath, although more or less may be found to be desirable, depending on operating conditions and whether used alone or in combination with other auxiliary addition agents as explained later.

The operating conditions depend on the type of plating being done and on the results desired, all of which is well understood by those skilled in the art. For example, in barrel plating the pH of the bath is usually around 5 to 6, and the temperature around 120 F., while in still plating the pH of the bath may vary from around about 2 to about 4 and the temperature from around about to about F. The art of nickel plating is fairly complex, and is disclosed rather fully in the book Modern Electroplating, hence a repetitious discussion is not required here. It is obvious to those skilled in the art, however, that it is not practical to specify exactly the operating conditions, bath composition and concentration of our new and novel brightening agent that should be used since all may well be varied by the user skilled in the art to secure the results desired in any given set of circumstances.

We have also found that our new and novel nickel plating brightener works synergetically with other nickel plating bath addition agents revealed in the prior art, such as, for example, the aryl sulfonamides and sulfonimides disclosed in US. Patent 2,191,813 and the plain and substituted aryl sulfonic acids disclosed in U.S. Patents 1,818,229; 1,972,693; 2,112,818; and 2,114,006.

In this connection, the addition agents of the general types disclosed in the aforementioned patents are not requisite in the bath to secure the bright nickel plate which is produced by polyacrylarnide alone, but their presence in the bath may be found to be desirable for auxiliary reasons, and they act synergetically with polyacrylamide to modify the physical characteristics of the nickel deposit to meet specific requirements of the user, as hereinbefore explained.

Without limiting ourselves to specific combinations or concentrations of bath ingredients as hereinbefore explained, we may cite the following bath formulation as illustrative of the type of combinations that we have found to be effective. The concentrations are only approximate.

Grams per liter Nickel sulfate, NiSO .7H O 250 Nickel chloride, NiCl .6l-I O 60 Boric acid, H BO 45 Polyacrylarnide 0.2 Benzosulfimide 1.0

Other similar combinations are obvious from the examples given herein and in the above identified patents. It may be found desirable, particularly in still plating, to incorporate a wetting agent into the bath formulation, such as, for example, sodium lauryl sulfate as taught in US. Patent No. 2,254,161. It could be added to plating baths of the foregoing formulations, for example, toproduce abath concentration of around 0.5 gram per liter. Since commercial operators of nickel plating baths 3 i make up their solutions of nickel salts quirements and then add a brightener, the most expedient manner in which this invention can be made available to them is to provide a composition of matter suitable for addition to nickel plating baths, which contains polyacrylamide alone or in combination with other ingredients compatible in nickel plating baths, and/or with other auxiliary addition agents as disclosed in prior references. The essential ingredient in every case is polyacrylamide. As examples .of the types of such products that would be useful, the following compositions may be cited:

1. Liquid nickel brightener This might well be an aqueous solution having the composition:

' Grams per liter Nickel, sulfate, NiSO .7H O Polyacrylamide 10 V 2. Mixed nickel plating brightener Parts by weight Polyacrylamide About Saccharin About 85 Such a mixture could then be dissolved in a nickel plat- I ing bath in the proportion of around one or two grams per liter of'plating bath, as required to produce the results desired. This corresponds to around one-eighth to one-quarter of an ounce of the mixture per gallon of nickel plating bath. Other similar mixtures are obvious from the patents hereinbefore mentioned.

It is also obvious that a suitable wetting agent could be incorporated into either or both of the above mixtures, if so desired, in accordance with the teachings of the reference cited. Insofar as this invention is concerned, however, the only important ingredient of any nickel plating bath brightener discussed herein is polyacrylamide.

3. Aqueous nickel brightener solution Grams per liter Polyacrylamide This solution is relatively concentrated by comparison with the polyacrylamide content of the usual bright nickel electroplating baths of this'invention so that, as in the foregoing examples, only a small portion of this solution is added to a relatively large volume of plating bath and the brightener solution is greatly diluted. Also, as in the foregoing examples, this aqueous brightener solution may conveniently be prepared and'marketed for electroplaters use in their standard nickel plating baths, the solution being easily measured and added directly to the plating solutions.

Those skilled in the art will understand in view of the foregoing that in one of its aspects the present invention, broadly described, relates to the method of preparation of an aqueous bright nickel electroplating bath which includes as an essential feature the step of dissolving polyacrylamide in a small volume of water to produce a concentrated solution for addition as a brightening agent to a relatively large volume of plating bath. They will likewise understand that this method may involve the step of dissolving polyacrylamide and a soluble nickel salt to meet their re- 4 I ferred embodiment of this procedural aspect of the present invention the step of dissolving polyacrylamide in water will be carried out so as to produce a solution which contains between about 1 gram of polyacrylamide per liter and an amount of said polyacrylamide representing the limit of its water solubility at room temperature. Such a solution then may be used in relatively greater or smaller amounts in preparing a plating bath to provide a polyacrylamide concentration in the bath in the optimum range stated above, i.e. between about 0.05 and about 0.50 gram per liter.

Having thus described this invention in such full, clear, concise and exact terms as to enable any person skilled in the art to which it pertains to make and use the same, and having set forth the best mode contemplated of carrying out this invention, we state that the subject matter which we regard as being our invention is particularly pointed out and distinctly claimed in what is claimed, it being understood that equivalents or modifications of, or substitutions for, parts of the above specifically described embodiments of the invention may be made without departing from the scope of the invention as set forth in what is claimed.

What is claimed is:

1. In the process of electroplating bright nickel from an aqueous solution of a nickel salt, the step comprising adding polyacrylamide to said solution in amount correspondingto between about 0.05 and about 0.5 gram per I liter.

in approximately equal quantities in water in order to 2; In'the preparation of an aqueous bright nickel electroplating bath, the step of dissolving in water between about one gram of polyacrylamide per liter and the maximum amount soluble in water at room temperature and an approximately equal amount of soluble nickel salt, and adding said solution to a plating bath in a concentration of about two ounces per gallon of the plating bath.

3. In the preparation of an aqueous bright nickel electroplating bath, the steps of dissolving in water at room temperature above about one gram of polyacrylamide per liter and an approximately equal amount of a soluble nickel salt, adding said solution to a plating bath in a concentration of abouttwo ounces per gallon of the plating bathand also adding to the plating bath about one gram per liter of beuzosulfimide.

4. A composition of matter for use in electroplating bright nickel comprising water having dissolved therein, at room temperature, a nickel salt and above about one gram of polyacrylamide per liter.

5. A composition of matter for use in electroplating bright nickel comprising water having dissolved therein, at room temperature, above about one gram of polyacrylamide per liter and an approximately equal amount of a nickel salt. a

6. A composition of matter for use in electroplating bright nickel comprising water having dissolved therein, at room temperature, above about one gram of polyacrylamide per liter, an approximately equal amount of a nickel salt, and several times as much saccharin.

7. A bright nickel electroplatingbath comprising an aqueous solution of a nickel salt and between about 0.05 and about 0.5 gram per liter of polyacrylamide.

References Cited in the of this patent UNITED STATES PATENTS 2,171,842 Barrett et al. Sept. 5, 1939 2,781,305 Brown Feb. 12, 1957 2,798,040 Pye et al. July 2, 1957 FOREIGN PATENTS 934,081 Germany Oct. 13, 1955 OTHER REFERENCES Raub et al.: Metal Finishing, June 1940, pp. 315-316. 

1. IN THE PROCESS OF ELECTROPLATING BRIGHT NICKEL FROM AN AQUEOUS SOLUTION OF A NICKEL SALT, THE STEP COMPRISING ADDING POLYACRYLAMIDE TO SAID SOLUTION IN AMOUNT CORRESPONDING TO BETWEEN ABOUT 0.05 AND ABOUT 0.5 GRAM PER LITER. 